RFID or radio frequency identification is a term characterizing a technology for the contactless transmission of identification features. An RFID-system comprises a transmission/receiver unit and an RFID-transponder. The transmission/receiving unit (RFID-reading device, RFID-terminal) can read out data stored in the RFID-transponder (also referred to as RFID-label or RFID-tag).
RFID-transponders exist in a great many configurations. The best known are RFID-transponders in the form of labels for attaching with adhesive or labels which are sewn in. In addition, there are RFID-transponders in the form of blocks or glass capsules for injections. RFID-transponders include a microchip having a memory and an antenna. RFID-transponders can be realized as active or passive. The antenna comprises, for example, a copper foil and can be especially well recognized in RFID-labels.
One distinguishes between active and passive RFID-transponders. Active labels have their own energy supply. Passive labels obtain their energy only from the electromagnetic field of the reading apparatus.
Data can be read out from an RFID-transponder via an RFID-reading apparatus. The read out function is contactless. Typical RFID solutions bridge distances of some centimeters up to several meters. The possible reading distance is dependent above all on the transmitting power of the RFID-terminal (reading apparatus) and the antennas used.
There is no uniform RFID standard which stipulates a specific frequency band. The frequency bands, which are available for use, differ from one country to another. Thus, different national and international solutions have developed. The following frequency ranges are distinguished:
a) 30 to 500 kHz (LF): in this range, cost effective systems are realized, for example, for access controls and controls to prevent unauthorized use in motor vehicles. Many solutions for time detection and access control operate at 125 kHz. The reading speed is relatively low.
b) 10 to 15 MHz (HF): solutions for identification in retail dealerships operate in this range. The label known as the smart label comprises an RFID-transponder and a barcode and operates at 13.56 MHz.
c) 850 to 950 MHz (UHF): in Europe, the range of 868 MHz to 870 MHz is authorized for RFID applications. The region about 915 MHz is not permissible in Europe as an ISM-band. In the United States and Australia, this band is, however, used for RFID. Some solutions in the area of logistics operate in the UHF range.
d) 2.4 to 2.5 GHz and 5.8 GHz (microwaves): in these ranges, so far hardly any practical solutions are present. In the free released bands, also wireless LAN-systems (WLAN) operate according to IEEE 802.11.
There are RFID-systems which operate with only one carrier frequency. So-called agile readers are reading apparatus which can operate at several frequencies.
The use of copper antennas is often not practical when the external appearance of the item equipped with an RFID-transponder is important such as a piece of jewelry or when the item, which has the RFID-transponder, itself has an optical function such as the glass of a watch or the mirrored surface of an optical apparatus.
In the meantime, the Swiss firm Winwatch offers wristwatches which are equipped with an RFID-transponder in order to, for example, carry out a payment without cash. This is possible via an RFID-chip of the Hitachi Company built into the watch glass. This so-called μ-chip is a complete RFID-transponder having memory for a serial number including 128 bits. What is decisive here is the size. The chip has an edge length of only 0.4 mm whereby it can be applied almost invisibly over the indicator aim axis of the watch. Building into the glass of the watch affords two advantages. The RFID-chip can, on the one hand, be built into every watch glass without it being necessary to change the inner workings of the watch. The glass can be manufactured with the RFID-chip and built in and, if necessary, also be retrofitted. On the other hand, the seating in the watch glass prevents the RFID-signal from being disrupted or attenuated by the metal housing. Notwithstanding the tiny dimensions, the chip has a complete antenna in the same manner as the larger versions thereof. The size, however, prevents the chip from being read out at far distances. For this purpose, the transmission power is not adequate. Furthermore, the visibility of the RFID-chip in the watch glass is found to be disturbing by users with this visibility being present notwithstanding the small dimensions of the RFID-chip.